In recent years, 2,3,3,3-tetrafluoropropene (HFO-1234yf) has attracted attention as a new refrigerant to replace 1,1,1,2-tetrafluoroethane (HFC-134a) which is a greenhouse gas. In this specification, with respect to a halogenated hydrocarbon, after its chemical name, an abbreviated name of the compound is shown in brackets, and in this specification, as the case requires, instead of the chemical name, its abbreviated name is used.
As a process for producing HFO-1234yf, for example, a process is known wherein 1,1-dichloro-2,2,3,3,3-pentafluoropropane (HCFC-225ca) is subjected to dehydrofluorination with an aqueous alkaline solution in the presence of a phase-transfer catalyst to obtain 1,1-dichloro-2,3,3,3-tetrafluoropropene (CFO-1214ya), which is then used as synthetic raw material and reduced by hydrogen to obtain HFO-1234yf.
However, this process has problems such that it requires multistage reactions whereby installation costs tend to be high, and distillation/purification of the intermediate product and the final product is difficult.
On the other hand, Patent Document 1 discloses that different types of hydrochlorocarbon compounds (e.g. chloromethane and chlorodifluoromethane) are combined and heated at 845±5° C. in the presence of steam for dehydrochlorination and condensation, whereby fluorinated olefins such as HFO-1234yf are formed.
Further, Patent Document 2 discloses a method for obtaining HFO-1234yf by heating and decomposing a mixture of chloromethane and tetrafluoroethylene (TFE) or chlorodifluoromethane at a temperature of from 700 to 950° C. by a common heating means such as an electric heater in a reactor.
However, in each of the methods disclosed in Patent Documents 1 and 2, although HFO-1234yf was formed by one reaction, it was not possible to obtain highly pure HFO-1234yf in sufficiently high yield, since the amount of a byproduct formed such as chlorotrifluoroethylene (CTFE) which is difficult to separate by distillation from HFO-1234yf, tended to be large.
Further, in the method disclosed in Patent Document 2, as the retention time increased, formation of high boiling products as by-products and carbonization of raw material were likely to occur whereby the reactor was likely to get blocked. Further, by the influence of an acid component formed as a byproduct, a special corrosion resistant apparatus (such as a reaction tube lined with platinum) was required, and thus, in consideration of the industrial production, such a method was totally unrealistic.